This invention relates to thermoplastic interlayer having rough surfaces and more particularly to a particular form of rough surface for optimum deairing in a prelaminate with glass.
Plastic sheet, typically of polyvinyl butyral (PVB), is known as an interlayer for use with optically transparent glass in laminated safety glass assemblies used, for example, in vehicle windshields, building windows and the like.
It is further known, (see, for example, U.S. Pat. No. 4,035,549, to Kennar) to make the surface of the sheet rough to facilitate deairing, i.e. evacuating air from an interface between the sheet and a glass layer during preparation of a prelaminate of the sheet with glass. More specifically, minute channels between the smooth surface of the glass and the rough surface of the opposing contiguous sheet form routes for air to escape from between the two members when pressure or vacuum is applied with heat during preparation of the prelaminate. The deaired prelaminate is then subjected to elevated temperature and pressure bonding conditions, usually in a downstream autoclave, to form the finished safety glass assembly.
Inadequate deairing results in visual defects in the finished safety glass assembly in the form of undesirable bubbles or local unlaminated regions. Deair completeness is conveniently measured by light transmission through the prelaminate before final laminating in the autoclave. The greater such transmission, the greater the quality of deairing provided by a particular profile of rough surface.
Optimum deairing is a continuing need in the laminated safety glass art.